Ecological Factors Influencing Population Dynamics of the Mississippi Sandhill Crane, Grus canadensis pulla

My dissertation encompasses three studies involving ecological factors influencing the Mississippi sandhill crane (Grus canadensis pulla) population at Mississippi Sandhill National Wildlife Refuge. To examine influences on the historical population I studied trends in nesting, number of chicks fledged annually, and their environmental and biotic drivers during 1991-2018. I expected precipitation to be positively associated with population measures and drought, extreme heat, and predation to be inversely related to population measures. To examine the influence of current habitat food production on the crane population I quantified measures of production in 2018 and 2019 and their relationship to time since an area was burned and crane population dynamics from 1991-2019. I expected measures of habitat food production to be positively associated with crane population measures and inversely related to time since burn. To examine the relationship between land cover, predation, and crane population I used geographic information system (GIS) analysis to classify land cover characteristics and relate those to crane population dynamics and predator trapping during 2018, 2016, 2014, and 2012. I expected to discover a decrease in chick fledging in areas with more edge habitat due to increased predation risk associated with habitat edges. Population size, number of nests, and number of chicks fledged annually increased significantly from 1991-2019. Total population size was positively related to nesting season precipitation, while the number of chicks fledged annually was negatively related to number of extreme heat days from June to August and estimates of bobcat occurrence. The number of chicks fledged annually occurred with approximately equal frequency across management units burned at different times prior to nesting. Herbaceous production bore no relationship to time since burn or arthropod production. Nesting was positively associated with orthopteran density, but number of wild-hatched chicks fledged annually was unrelated to the production of vegetation or arthropods. I detected no increase in predation related to habitat edge effect. The results indicate that both biotic and abiotic factors drive population dynamics on the refuge and suggest that continued attention to prescribed burns and predator removal is necessary for the establishment of a self-sustaining wild population in the future